Colon: impaction

Etiology

• Most colonic impactions occur in the large colon, particularly at the pelvic flexure and right dorsal colon. Impactions arise most commonly at sites where there is transition of intestinal movement, at sphincters between different segments of intestine, or at regions of intestinal narrowing. The causes in many cases remain unknown but possibilities include:
  • Poor teeth and thus poor mastication of food.
  • Stress associated with transport, etc.
  • Inadequate or inappropriate food (coarse roughage).
  • Parasitism.
  • Systemic dehydration.
  • Eating of bedding or other inappropriate material that is poorly digested.
  • Gastric ulceration, intestinal adhesions.
  • Lack of sufficient water.
  • Sudden change in management, especially exercise or diet.
• Cases are particularly common in horses that are suddenly put onto box rest, in many cases these are fit animals who are on high rations. Change in feed rations and boredom encourage them to eat their bedding.
• Sub-acute grass sickness Grass sickness.
• Infrequent feeding.
• Damage to colonic nervous system due to previous colonic distention affecting colonic motility.
• Small colon impactions can occur for the same reasons, but many are idiopathic. Interestingly, one survey showed 25% of those horses that went to surgery for correction of a small colon impaction were Salmonella positive.
• See Rectum: meconium impaction.
• Acquired narrowing of the colon due to trauma, neoplasia, or previous surgery.

Predisposing factors

General

• Recent change in environment or regime.
• Poor dentition.
• Inadequate, inappropriate or poor quality feeding.
• Parasitism.
• Decreased or lack of sufficient water.
• Travel and stress.

Pathophysiology

• Inadequately digested food matter (or foreign bodies) accumulates in colon. Though properly digested, good quality food matter can also become dehydrated and impacted with decrease water intake and decreased motility.
• A blockage of the intestinal lumen results.
• The impacted ingesta becomes progressively harder and drier with time, and thus more and more solid.
• Peristaltic waves may become weaker due to the presence of a blockage.
• Dehydration may occur due to decreased eating and drinking.
• Poorly understood.
• Impactions tend to occur at sites where there is physical change in: Either The course of the gut lumen, so a partial 'kink' is present, encouraging ingesta to build up. Or Size of gut lumen, ie pelvic flexure and transverse colon. Or due to a pre-existing luminal obstruction such as enterolith or tumor.
• Abnormal gut motility may be as important in the development of this disease as the character of ingesta.
• Poor GI motility can occur on box rest, since exercise promotes peristaltic activity. Other factors such as lack of fresh grass can be involved.
• Horses living in a sandy environment may slowly eat and accumulate sand within their colon which gradually creates a narrowing of the lumen and predisposition for obstruction Gastrointestinal: sand colic.
• Correlation with presence of Salmonella Salmonella spp may also be associated with that organism's effects on gut motility.

Timecourse

• Usually a chronic timecourse, involving a gradual build-up of the impaction within, and then a gradual worsening of symptoms. If more serious sequela result, the presentation can even appear to be acute.